German testers have used a 70km dash down the autobahn to show just how uneconomical high-speed driving can be.
The tests show some cars consume more than 60 litres of fuel per 100 kilometres when driven at top speed.
In all, ten cars from eight manufacturers were assessed by experts from the publication Autobild.
The thirstiest was the outrageously fast Jaguar XFR-S. Its V8 engine burned 62.5 litres per 100 kilometres when driven at its full tilt of 300km/h.
This is more than five times its average consumption of 11.6 litres.
The angular Mercedes-Benz G 500 SUV, one of the least aerodynamic cars on the road, proved to be equally thirsty.
Average consumption of 14.9 litres per 100km quadrupled to 62.3 litres when driven at full belt.
It was a similar story with the BMW M5, which consumed 62 litres at full speed - a sixfold increase over standard consumption.
When driven hard, diesel-powered cars remained fairly frugal compared with their petrol equivalents.
The Skoda Octavia 1.2 TSI estate used 13.4 litres, over double the normal 5.1 litres. The VW Golf 2.0 TDI burned 14.6 litres instead of an average 4.1 litres.
